Putting the "Lift" into Liftboats

Wednesday, November 20, 2002

In the strictest sense, a liftboat is a self-propelled crane barge that can elevate itself above the water line. It is the cranes that make a liftboat such a valuable tool for building and/or renovating offshore oil and gas structures. A recent example of the working ability of these liftboats is the L/B Myrtle, a 137.5-ft. by 92-ft. vessel with a trio of 245-ft. legs, enabling the vessel to work in water depths of 180 ft. with a 15-ft. air gap. The vessel was built by Bollinger Shipyards in their Lockport facility and sent to Bollinger's Amelia, La. shipyard for the outfitting of the three legs.

Montco Offshore, Inc., Galliano, La., owns the vessel. Montco owns six liftboats capable of operating in water depths from 75 to 180 ft. and offer these vessels to a wide variety of Gulf of Mexico clients.

The vessel carries three Nautilus cranes, built by Applied Hydraulic Systems, Inc., Houma, La. with 150, 50 and 25-ton capacities. The cranes are arranged on the deck of the M/V Myrtle, so the smaller 25-ton crane can be use to load supplies and personnel from other vessels and not disturb the work being done by the two larger cranes. In effect, the 25-ton crane serves the lift boat, while the two larger cranes do the project work.

While all three of the cranes onboard the Myrtle are of different designs with greatly different lifting capacities, all are hydraulic powered.

Power from a diesel engine drives a multi-section hydraulic gear pump that powers the main hoist, auxiliary hoist, swing of the crane and the boom hoist or boom cylinder. The engine sits on a two-section tank holding the hydraulic oil reservoir and the diesel fuel for the engine.

The 25-ton crane serving the liftboat has a 70-ft. box beam crane arm. Its main hoist has 677 ft. of 5/8-in. wire rope and has a hook speed of 27-50 ft. per minute depending on the number of parts or loops the line makes through the upper and lower pulleys above the hook

The auxiliary hoist has 231 ft. of 5/8-in. wire rope and a hook speed of 207 ft. per minute but its lifting capacity is limited. The auxiliary hoist would be used for a quick lift of personnel from a vessel that may be pitching in the water.
Cranes in this class use a boom or luffing cylinder to lift the crane boom. On this crane, a pair of 10-in. boom luffing cylinders lift the crane boom.

The swing drive on this crane can make up to 1.5 complete revolutions per minute for crane positioning.

A Caterpillar 3408 engine is used to power this crane. This engine along with its associated components such as the hydraulic gear pump, oil reservoir and diesel fuel tank are located in the hull of the liftboat. This engine also powers the 50-ton crane.

The 50-ton box crane is unique among the three cranes in that it has a boom that retracts from full extension of 70 ft. down to 50 ft.. A pair of 8-in. hydraulic cylinders powers the extension of the boom. The crane features continuous 360-degree rotation at up to 1.5 revolutions per minute regardless of the degree of extension. A pair of 12.5-in. luffing cylinders lifts the crane boom. It also features main and auxiliary hoists. The rigging for the hoists is 1,200 ft. of 7/8-in. wire rope for the main hoist that can lift 50 tons and the hook can travel from 14 to 56 ft. per minute based on the line parts through the upper and lower pulleys.

The auxiliary hoist has a one-part line for a minimum hook speed of 210 ft. per minute and holds 306 ft. of 5/8-in. wire rope.
The real workhorse of the L/B Myrtle is the Nautilus 150-ton lattice boom crane. The boom is 110 ft. long and is of lattice beam construction. The boom of the crane is raised and lowered by a 40-ft. high gantry using two 55-ft. 2.5-in. diameter pendant lines and 1,050 ft. of 1.125-in. wire rope made up in a 10-part line.

The main hoist rigging consists of 3,020-ft. of 1.125-in. wire rope made up in a 10-part line yielding a hook speed of 12 ft. per minute. The auxiliary hoist can lift 10 tons at a hook speed of 128 ft. per minute using a two-part line.

To provide the power this crane needs, a Caterpillar 3408 diesel is dedicated to this crane and is located along the centerline of the crane. The hydraulic system for this crane has a dual drive gearbox that powers two three-section gear driven hydraulic pumps. Two of the pumps feed the boom, two power the main winch hoist, one is for the auxiliary hoist and one for the swing drive system.

The hydraulic system features a 1,000-gallon hydraulic oil tank. A 300-gallon diesel oil tank supplies fuel to the engine. The pedestal of this crane rises about 10-ft. about the deck of the liftboat.

A fully insulated and air conditioned cab is located on the starboard side of the crane and is equipped with a radio, loudhailer, load indicator and boom-mounted video camera to assist with hookups out of the normal view of the operator.

"The choice of the cranes and their positioning is another indicator of the work Montco and Bollinger did to design the most efficient crane possible", said Dr. Joe Orgeron, chief technology officer of Montco Offshore, Inc.

The company is the leading supplier of cranes for vessels and structures in the Gulf of Mexico and to date has manufactured over 1,100 cranes in operation worldwide. "Our cranes are used on TLP's, SPARS, FPSO's offshore platforms and a wide variety of offshore service vessels and dockside mount applications," added J. W. Roddy, project manager for the company.

The liftboat was delivered about two months ago and has already seen extensive work. One of its first projects was to transport and deliver two prefabricated buildings to a platform that is a part of the Louisiana Offshore Oil Port (LOOP). "The available deck space and crane capacity made this a very successful beginning for the L/B Myrtle," Orgeron said.